What kind of eye defects do double merles have?
Dogs that inherit two copies of the merle gene (“double merles”), usually have multiple eye defects, generally with associated vision loss which often goes to the point of blindness. Any part of the eye can be affected. Irises are frequently deformed, sometimes grossly so. Pupils may be subluxated (off-center). The lens may be subluxated (out of place). The retina may be abnormal, and the optic nerve may be improperly developed. The entire globe of the eye may be abnormally small (microphthalmia). Most double merles will have one or combination of these defects in each eye. All of this can be avoided by not breeding merle dogs to each other.